Like a dice, the cube has six faces; but instead of numbering 1-6, they number 2, 4, 8, 16, 32, and 64. The game commences with the 64, i.e. with that side facing upwards. The cube is placed in the middle of the table in a position equal distance between the two players. Once the worth of a single unit has been determined, the first double raises the stakes from 1 to 2; the next double from 2 to 4; and so on. If the cube rises to 64 in a particularly aggressive game, the next double will revert back to 2 (but in fact will represent 128)

There are two ways in which doubles can be made.

• An automatic double usually occurs when both players have thrown the same number with their opening single dice. This manner of play is not adopted in tournaments, and you must be wary of the opponent who wants to play an unlimited number of automatic doubles (i.e. not only when each player throws his single dice, but also when doubles are repeated or the opponent throws a double with his first throw). Normally one automatic double is the accepted order of the day. You must remember that three doubles will increase the count form one to eight. You may have wo0n five long, drawn out games in succession, and be five points up, only to lose the next one and be three points down overall.
• A voluntary double is simply when one player offers his opponent the option of accepting or refusing a doubling of the stakes. If he refuses, he forfeits the game along with whatever is showing on the cube at the time of the offer. If he accepts, the stake is doubled and the game continues. A player can only offer a double when it is his turn to play and before he has rolled the dice.

Many players fail to appreciate the advantages of being in possession of the cube. When you are in possession, you are the only one who can redouble, and thus you control the game form a financial point of view. The stakes cannot be raised unless you wish them to be.

There are normally three situations in which one player will offer the other a double:

(a) if, in a running game, his men have less distance to travel than those of his opponent;

(b) when he has built a block and his opponent is unable to escape (he must however be mindful that if the double is refused, he may have missed the opportunity of winning a double game);

(c) if, in the final stages of the game, he is bearing off and his pip count is less than his opponent's.

In a running game it is important to be aware of when to accept, refuse or indeed offer a double. The more experienced players work out the difference in the pip count and consequently adopt the following formula, known as the rule of fifteen.

Add up your own and your opponent's pip counts, and work out the difference. If the difference is less than 15% a double should be taken; if more a double should be refused. For example, if your pip count is 50 and your opponent's 60, the difference is ten ( or 20%). It is clear that in this case a double should be offered but refused.

Too often an experienced player accepts a double form a less experienced opponent because he thinks that the latter's good luck in throwing the dice will not last and that he is in any case prone to making mistakes. This is a dangerous attitude to adopt, and the rule of 15 should be strictly observed.

Whilst bearing off, the distribution of the pieces can have an influence on whether you offer, refuse or accept a double. In certain circumstances the rule of 15 can be misleading. A board which has men equally distributed across the points is much stronger  when bearing off than one with an accumulation of men on one or two points.